The present invention relates generally to the field of synthesizing a tone waveform, and more particularly to a tone synthesizing apparatus and method using an arithmetic processor such as a CPU and a dedicated tone generator device such as a tone generator LSI circuit.
With recent improvements in arithmetic processing capabilities of CPUs, tone synthesizing systems have been developed which use a CPU to execute a program descriptive of processing for generating performance information (e.g., a sequence program descriptive of automatic performance processing) as well as a program descriptive of tone synthesizing processing (based, for example, on the well-known waveform memory or FM technique) responsive of the performance information generated by the performance information generating processing. These tone synthesizing systems have the advantage that they can synthesize a tone waveform using compact and low-cost circuity without requiring a particular dedicated tone generator device such as a tone generator LSI circuit. Thus, the tone synthesizing systems have been widely used today not only in CPU-equipped electronic musical instruments and computer music systems provided with a personal computer but also in CPU-equipped karaoke devices, game machines, teaching equipment, etc.
Unlike the dedicated tone generator device, the CPU must execute various other processing than the tone synthesizing processing, such as those for an OS (operating system) and other application software. For this reason, an undesirable time delay tends to occur due to the fact that initiation of the tone synthesizing processing has to be delayed, even when performance information is supplied, if execution of other processing is under way at that time, or that the tone synthesizing processing has to be temporarily stopped in order to execute an interrupt process during execution of the processing. To provide a solution to the problem, more sophisticated tone synthesizing systems have been proposed, in which a given allowance time sufficiently longer than an expected delay time is preset as an extra period for the tone synthesizing processing so that transfer of tone waveform data to a sound system is initiated upon lapse of this allowance time; thus, in this case, it is only necessary for the CPU to complete synthesis of a predetermined number of tone waveform samples within the sufficiently long allowance time. With such an arrangement, some of the sophisticated tone synthesizing systems are capable of executing performance of a music piece or the like at uniform tone generation timing irrespective of different delay times occurring in the tone synthesizing processing based on individual performance information.
As mentioned above, the tone synthesizing systems which have their CPUs execute the tone synthesizing processing have the superior advantage that a tone waveform can be synthesized with compact and low-cost circuity without requiring a particular dedicated tone generator device such as a tone generator LSI circuit. However, the number of simultaneously generatable tones and tone colors that can be synthesized by the CPU alone may be substantially limited depending on the CPU's arithmetic processing capability, particular specifications of the tone synthesizing processing program, etc. For this reason, it is desirable to further increase the number of simultaneously generatable tones and variations of tone colors in cases where such a tone synthesizing system is employed. One approach to realize such a performance may be to additionally provide a separate dedicated tone generator device so that both the CPU and the dedicated tone generator device perform a same music piece (i.e., ensemble) by executing the tone synthesizing processing together.